Software fuel volatility measurement

ABSTRACT

A system is described using a fuel quality sensor or an estimate of fuel volatility for controlling various aspects of engine operation. For example, improved fuel tank leak detection may be achieved using an estimate of fuel volatility obtained from fuel purging operation.

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/065,362, filed Oct. 9, 2002, the entire contentsof each of which are incorporated herein

BACKGROUND AND SUMMARY

Determination of fuel volatility may be useful for various aspects ofengine control and diagnostics. While sensors may be used, the inventorherein has recognized an advantageous approach for estimating fuelvolatility in place of, or in addition to, other detection techniques.

In one example, it is possible to determine the fuel volatility and/orcombustion characteristics based a rate of change of vapor generationduring fuel vapor purging operation. In one example embodiment, the rateof change of vapor generation, (which may be normalized based on massair flow, manifold pressure, or other parameters to reduce the effect ofvariable flown a sensor) can be used to enable diagnostic fuel tankoperation after the engine is stopped. In this way, it can be possibleto reduce errors in degradation detection. For example, in the casewhere a sealed fuel tank is checked for leaks based on environmentaltemperature changes, changes in pressure due to high fuel volatilitythat may mask such leaks can be identified. Furthermore, a improvedmeasurement or estimate of fuel volatility can be used for other enginecontrol purposes as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment used to advantage;

FIGS. 2A-C are schematic diagrams of an example acoustic wave fuelquality sensor;

FIGS. 3-4 are graphs illustrating sensor output for use with the presentdisclosure;

FIGS. 5-6 show experimental data illustrating the relationship betweenviscosity, density, and DI;

FIGS. 7-14 are high-level flow charts of various operations;

FIG. 15 is a graph illustrating transmission of the acoustic wave;

FIG. 17A is a graph showing operation according to one embodiment; and

FIG. 17B is a high level flow chart for learning fuel quality.

DETAILED DESCRIPTION

Internal combustion engine 10 comprises a plurality of cylinders, onecylinder of which is shown in FIG. 2. Electronic engine controller 12controls Engine 10. Engine 10 includes combustion chamber 30 andcylinder walls 32 with piston 36 positioned therein and connected tocrankshaft 13. Combustion chamber 30 communicates with intake manifold44 and exhaust manifold 48 via respective intake valve 52 and exhaustvalve 54. Exhaust gas oxygen sensor 16 is coupled to exhaust manifold 48of engine 10 upstream of catalytic converter 20.

Intake manifold 44 communicates with throttle body 64 via throttle plate66. Throttle plate 66 is controlled by electric motor 67, which receivesa signal from ETC driver 69. ETC driver 69 receives control signal (DC)from controller 12. Intake manifold 44 is also shown having fuelinjector 68 coupled thereto for delivering fuel in proportion to thepulse width of signal (fpw) from controller 12. Fuel is delivered tofuel injector 68 by a conventional fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown).

Engine 10 further includes conventional distributorless ignition system88 to provide ignition spark to combustion chamber 30 via spark plug 92in response to controller 12. In the embodiment described herein,controller 12 is a conventional microcomputer including: microprocessorunit 102, input/output ports 104, electronic memory chip 106, which isan electronically programmable memory in this particular example, randomaccess memory 108, and a conventional data bus.

Controller 12 receives various signals from sensors coupled to engine10, in addition to those signals previously discussed, including:measurements of inducted mass air flow (MAF) from mass air flow sensor110 coupled to throttle body 64; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling jacket 114; a measurement ofthrottle position (TP) from throttle position sensor 117 coupled tothrottle plate 66; a measurement of turbine speed (Wt) from turbinespeed sensor 119, where turbine speed measures the speed of shaft 17;and a profile ignition pickup signal (PIP) from Hall effect sensor 118coupled to crankshaft 13 indicating and engine speed (N).

Continuing with FIG. 1, accelerator pedal 130 is shown communicatingwith the driver's foot 132. Accelerator pedal position (PP) is measuredby pedal position sensor 134 and sent to controller 12.

In an alternative embodiment, where an electronically controlledthrottle is not used, an air bypass valve (not shown) can be installedto allow a controlled amount of air to bypass throttle plate 62. In thisalternative embodiment, the air bypass valve (not shown) receives acontrol signal (not shown) from controller 12.

Continuing with FIG. 1, a fuel tank 140 is shown for containing fuelused to operate engine 10. Pump 148 is shown inside the fuel tank 140for pressurizing liquid fuel in fuel line 142. Fuel line 142 deliverspressurized liquid fuel to fuel injector 68 which, as described aboveherein, is controlled by a signal (fpw) received from controller 12.Fuel pressure regulator 152 is also shown for regulating pressure infuel line 142. Regulator 152 is a mechanical pressure regulator valve.

A fuel vapor management system is also shown in FIG. 1 coupled to fueltank 140 and engine 10. In particular, fuel vapor line 154 couples thefuel tank to the intake manifold 44. A purge control valve 156 is alsoshown receiving a signal from controller 12. As described below herein,controller 12 adjusts purge valve 156 to control air and fuel vaporentering manifold from the fuel system based on engine operatingconditions. Continuing with the fuel vapor system, the fuel tank isshown coupled to a first and second carbon canister 144 and 146. Fuelvapors entering the engine 10, from fuel tank 140 first pass through thefirst fuel vapor carbon canister 146. Carbon canister 146 absorbs fuelvapors and desorbs fuel vapors depending on vapor concentration. Thesecond carbon canister 144 is coupled downstream of the fuel tank vialine 150. A solenoid valve may optionally be included in or coupled tocanisters 144 and 146, if desired, to block flow through the respectivecanisters.

The first and second carbon canister may optionally be replaced with aparallel configuration canister, such as third canister 147 with valve149. Alternatively, all three canisters may be used, or only one or twoof the three canisters may be used.

Finally, fuel quality sensor 160 is shown in fuel tank 140. In thisparticular embodiment, sensor 160 is in fluid contact with liquid fuelstored in fuel tank 140. Sensor 160 provides a signal (FQ) to controller12. As described below and with particular reference to FIG. 2, sensor160 is a surface acoustic wave device operating at approximately 100megahertz. In general terms, this sensor provides a signal related toviscosity and density of the liquid fuel stored in tank 140.

According to the present disclosure, fuel quality sensor 160 can belocated in various different positions on the fuel system/engine system.As an example, fuel sensor 160 can also be coupled to fuel line 142. Thesensor can be located either upstream or downstream of pressureregulator 152. Sensor location depends upon various factors, such as,for example, measuring the fuel near the point of fuel delivery,measuring fuel with minimal changes in fuel temperature, and variousothers.

In addition, a dielectric sensor 162 is shown for measuring liquid fuelin tank 140. The dielectric sensor output is typically utilized todetect the ethanol content of gasoline fuels. Further, intake airtemperature sensor 119 is shown coupled to intake manifold 44 formeasuring a temperature of the intake air and providing a signal (ACT)to controller 12.

Referring now to FIG. 2, details of sensor 160 are described. Sensor 160is a surface acoustic wave device, operating at approximately 100megahertz. The acoustic wave generated by the device interacts with theliquid fuel in which is contacting the device. The more viscous theliquid fuel, the more the propagation speed is changed and the more theacoustic wave is attenuated. By placing an electronic amplifier betweeninput and output of the surface acoustic wave delay line, an oscillatoris obtained. The oscillation frequency and electronic gain needed foroscillation on both measures for the viscosity (related to propagation,velocity and attenuation, respectively).

In addition, the surface acoustic wave device is covered by a thin layerof silicon dioxide. The wet cell (with liquid fuel) is placed on top ofthe delay lines, thereby allowing a leak-free connection secured with a14 millimeter viton o-ring. The sensor output, (a frequency signal inmegahertz in this particular example) provides an indication of dynamicviscosity times density.

According to the present disclosure, this signal (related to dynamicviscosity times density) correlates to fuel quality of liquid fuelcontained in the fuel system coupled to the engine. In other words, thesensor output can be correlated to the “drivability index (DI)”typically utilized to characterize fuel quality for engine combustion.Various forms of the sensor output can be used, as described below,including frequency, phase, amplitude, or propagation velocity.

Sensor 160, in one embodiment, can be based on a micro-acoustic (LOVE)waves the property through a thin wave guide material deposited on apiezoelectric substrate. One example of the device is described in“Viscosity Sensing Using LOVE wave devices” by B. Jakoby and M. J.Vellekoop in Vol. A68 of Sensors and Actuators (1998) pgs 275-281. Whenthe sensor is in contact with liquid fuel, the propagation losses andthe phase velocity of the LOVE wave change as a function of theviscosity-density product of the fuel. The sensor size is typicallyapproximately 8×4 millimeters. Since viscosity is dependent ontemperature, the sensor measures and corrects for this temperature.Alternatively, a separate temperature sensor can be used and thecorrection performed in controller 12. In other words, the device can betemperature compensated by measuring the temperature and compensatingfor this measurement. Alternatively, or in addition, a dual delay linecan be used, where only one is exposed to the liquid and the other not,but both are exposed to the same temperature. Besides the devicetemperature dependence, there is also temperature dependence in theviscosity-density of the liquid. Here, the temperature can be measuredand the measurement can be compensated as described above.Alternatively, or in addition, the device can be heated to a constanttemperature and the liquid probed by the device is heated to that sametemperature. If measurements are always performed at the sametemperature, no further compensation would be used.

The sensor 160 can have various outputs including a shift in oscillationfrequency, or a change in acoustic attenuation as measured by theelectronic gain required for the oscillation.

As indicated, various types of acoustic waves can be generated on or ina piezoelectric material. This acoustic wave propagating in or on thesubstrate then interacts with a liquid adjacent to the substrate to“probe” the properties of that liquid. These include, but are notlimited to: thickness shear mode resonator, flexural plate wave device,acoustic plate mode device, and Love wave sensors. The LOVE wave sensoris a described in detail since it has a simple and rugged design.

Referring now to FIGS. 2A through 2C, and specifically to FIG. 2A, aschematic diagram of a viscosity sensing LOVE-wave device is shown. Inthis example of sensor 160, an isotropic guiding layer of silicondioxide (210) is deposited on a substrate 212. Piezoelectric ST quartzis the substrate material 212, where the propagation direction is chosento be orthogonal to the crystal X direction. Interdigital transducers(IDT_(s)) 214 enable electrical excitation and reception of theLOVE-wave. The interdigital transducers 214 are embedded at theinterface between the layer 210 and the substrate 212. The IDTs convertan electric signal into an acoustic wave.

As described above, the propagation direction is chosen to be orthogonalto the crystalline X direction. This orientation allows the excitationof sheer polarized modes by the interdigital transducers 214. Theguiding layer 210 is deposited on the substrate by using plasma enhancedchemical vapor deposition. The acoustic energy associated with thepropagating wave becomes concentrated in layer 210. This allowsincreased sensitivity with respect to surface mass loading. The topsurface of layer 210 is in contact with the liquid fuel contained intank 140, in one example. Additionally, shielding 216 can be placed overguiding layer 210. In one example shielding 216 is a metal layer. Thedelay line is used as a frequency determining element and an oscillatorcircuit. In other words, it changed in the delay time due to the sensingfrom the transducers can be observed by monitoring oscillation frequencyas described below herein.

In addition, FIG. 2A shows a source 211 coupled to one of thetransducers 214 and a load 213 coupled to the other of the transducers214.

In general, the change in frequency as the viscosity-density of theliquid changes can be the sensor output. This change in frequency isrelated to the change in the propagation velocity of the acoustic wave.Alternatively, the change in damping of the acoustic wave can also bemeasured by the amount of electronic amplification that is needed tokeep the device oscillating.

Referring now to FIG. 2B, a side view of the sensor 160 is illustratedusing schematic diagrams. In particular, a wet cell 220 is shown mountedon the device, which allows the liquid fuel to contact only the regionbetween the interdigital transducers 214. Wet cell 220 can be attachedusing adhesive and sealing materials such as silicon rubber. Analternate approach would utilize a micro machined wet cell attachedusing fusion bonding techniques.

Next, FIG. 2C shows the device coupled to analog circuitry to generatethe sensor output. In FIG. 2C, the circuitry allows the determination ofthe affects of viscosity on the phase shift via measuring acorresponding change in frequency. Further, the control voltage of theautomatic GAIN control is monitored for a constant output level. Inparticular, FIG. 2C shows the output delay line 230 from theinterdigital transducers 214 coupled to a first amplifier 232. Further,a GAIN control amplifier 236 is used with a fixed reference levelvoltage. Further, the oscillator output is also fed to a DC/AC converter238 and then to amplifier 236. The output of amplifier 236 is fed toamplifier 232. Further, the output of the GAIN control 242 provides theautomatic GAIN control voltage readout which can be monitored. Further,the oscillator output is first buffered via amplifier 234 and thenprovides frequency readout 240 which can be used to determine fuelviscosity times density. The relation between the frequency change(ΔF/F) and the relative change in the wave number (Δβ/β) is given by thefollowing equation:ΔF/F=−V _(g) /V _(p) ×ΔB/BWhere V_(g) and V_(P) denote the group and phase velocity of the LOVEwave.

Delta B/B is the relative wave number change evaluated at constantfrequency. Complete details of calibration and calculations using thesensor in FIGS. 2A through 2C can be determined from the referencetitled “Viscosity Sensing Using a LOVE-wave Device” by Bernard Jakobyand Michael J. Vellekoop, Vol A68 of Journal Sensors and Actuators(1998) pages 275-281.

As described above, the details shown in FIGS. 2A to 2C show one exampleembodiment where acoustic energy (waves) are utilized to obtaininformation about the gasoline fuel fed to the engine. However, thepresent inventors have contemplated various other embodiments. Forexample, as described below here with particular reference to FIGS.11-14, and 17, one could also estimate fuel quality, or volatility, orviscosity, using estimates based on other sensors in the engine/vehiclesystem. Further, different sensor types could be used where differentenergy types are introduced into the fuel, such as light energy.

Referring now to FIG. 3, the graph shows output of sensor 160 versusoutput of sensor 162 for various different fuels. The first groupinglabeled “normal” fuels illustrates variation and sensor output acrossfuels that typically result in normal engine cold starts. The graphillustrates the different fuels both with and without ethanol. The graphalso illustrates type 1 fuels on the lower left hand side indicating alow sensor output from sensors 160 and 162. These fuels are sometimesknown as “hesitation” fuels in that they result in a lean combustionduring engine cold starting compared with the normal fuels. Finally,FIG. 3 illustrates a type 2 fuel which typically results in a richcombustion compared to the normal fuels. For these type 2 fuels, sensor160 provides an increased sensor output. As illustrated in FIG. 3, inone embodiment when controller 12 receives a signal (FQ) from sensor 160during an engine start, the controller adjusts the amount of fueldelivered via injector 68 based on the output of sensor 160. When thesensor 160 provides an output indicative of a normal fuel, controller 12simply provides the scheduled amount of fuel via injector 68 during theengine start. However, if sensor 160 provides an output greater thanapproximately 110.202 megahertz, the routine reduces the amount ofscheduled fuel to be delivered via injector 68 thereby preventing anoverly rich mixture. Similarly, when sensor 160 provides an output lowerthan approximately 110.913 megahertz, controller 12 adds additional fuelduring the cold start to be delivered by injector 68, thereby preventingthe combustion from being too lean. In this way, more consistent enginecold starting can be achieved even when large variations in the fuel areexperienced. This method, along with alternative embodiments, isdescribed more fully with regard to the routines described below.

Referring now to FIG. 4, the graph illustrates sensor output of sensors160 and 162 with different levels of ethanol. In particular, the graphillustrates that sensor 160 provides a high sensor output forhydrocarbon and fuels containing approximately 10% ethanol. However, formethanol fuels (approximately 85% ethanol) sensor 160 provides arelatively low sensor output. In this way, sensor 160 can be used todetect the type of fuel in vehicle. In particular, according to thepresent disclosure, controller 12 can determine whether the vehicle isoperating with methanol based on sensor 160.

As described above, output from sensor 160 can be utilized as anindication of the drivability index (DI). The drivability index istypically determined based on the following equation:DI=1.5×T ₁₀+3×T ₅₀ +T ₉₀Where T_(x) is based on the ASTMD-86 distillation curve.

When oxygenates are present in the fuel the correction to the DI is asfollows:DI=1.5×T ₁₀+3×T ₅₀ +T ₉₀+20*(weight %02) ° F.

Typically, a high DI is indicative of a poor drivability fuel (poorcold-start), resulting in combustion too lean of stoichiometry.Conversely, a low DI can indicate poor driveability in that thecombustion is too rich of stoichiometry.

This Driveability Index (DI) in one method to characterize fuel quality.DI correlates well with the cold-start driveability.

FIGS. 5 and 6 illustrate DI data versus dynamic viscosity times densityfor various hydrocarbon fuels contained in the American AutomobileManufacturer's Association 1996 survey data. Also note that a correctionfor ethanol fuels and methanol fuels can be used. Typically, a 10% EtOHresults in a correction of approximately 70 points in DI. Further, a 10%MTBE typically results in a correction of approximately 35 points in thedrivability index.

As shown in FIGS. 5 and 6, a relatively consistent correlation betweenthe drivability index and the dynamic viscosity times densitymeasurement is obtained. As shown in FIG. 6, this correlation is alsotrue including both summer and winter hydrocarbon fuels.

The following is a potential explanation of why such measurementscorrelate to drivability index and, thereby, to combustion quality.Drivability can be affected by the degree of fuel atomization during thecombustion process. The more effective the fuel atomization is, thesmaller the mean fuel drop in size can be and the higher the rate ofevaporation and mixing with the combustion air can be. For a fixedgeometry of the fuel injector and a constant fuel pressure and air flowand density, the atomization is influenced by properties of the liquidfuel such as, for example: fuel density, fuel viscosity and surfacetension. In addition to atomization, the spray angle can also beinfluenced by the density and viscosity of the fuel. Thus, measuringfuel viscosity and density can give an indication of the fuel quality.

Referring now to FIG. 7, the routine is described for controlling fuelinjection during an engine start based on the fuel quality sensor.First, in step 710, the routine determines whether the engine iscurrently starting. In particular, in step 710, the routine determineswhether the engine is in either the crank mode, or the initial run-upmode where engine speed increases rapidly to the desired idle rpm speed.When the answer to step 710 is “no”, the routine continues to step 712where injected fuel is controlled based on the desired idle speed andmeasured idle speed.

When the answer to step 710 is “yes”, the routine continues to step 712to determine a base fuel amount (fuelb) based on the engine coolanttemperature (ect), times since engine start, and intake air temperature(act). This base fuel amount is stored in lookup tables and calibratedover various engine conditions to achieve a reliable engine start.However, variations in fuel quality can cause degraded engine startsusing this base fuel amount. In particular, variations in the fuel typecan cause engine combustion to be either too lean or too rich, therebycreating poor engine startability and degraded drivability.

Note that the base amount of fuel can also be determined based on adesired torque. The desired torque can be determined from the operatorof the vehicle, or from a controller. Further, the desired torque can bebased on the pedal position.

Continuing with FIG. 7, in step 714, the routine reads the sensor output(FQ) from sensor 160, which is indicative of fuel viscosity and density.Note, that in an alternate embodiment, the routine can simply measureeither fuel viscosity or fuel density individually, or can simplymeasure fuel viscosity alone to provide an indication of fuel quality.Next, in step 716, the routine determines whether the parameter FQ readfrom sensor 160 is between a lower limit (L1) and an upper (L2). When FQis less than or equal to L1, the routine continues to step 718. When FQis between L1 and L2, the routine continues to step 720. Finally, whenFQ is greater than or equal to L2, the routine continues to step 722.

In step 718, the routine increases scheduled fuel amount by Δ2.Alternatively, in step 722, the routine decreases a scheduled fuelamount by Δ1. Finally, in step 720, no adjustment to the fuel deliveredbased on sensor 160 is used. From either 718, 720 or 722, the routinecontinues to step 724 to adjust the ignition timing based on the signalFQ. In one embodiment of step 724, the routine adjusts the location ofborderline spark based on the fuel viscosity.

In this way, the routine adjusts the injected fuel amount to account forvariations in the fuel quality and thereby achieve improved enginestarting. Specifically, when the signal FQ indicates a high signal (forexample greater than 110.202 megahertz), the routine decreases injectedfuel since the sensor indicates that combustion may be too rich.Conversely, when sensor 160 indicates a low output (for example lessthan 110.193 megahertz) the routine increases the scheduled fuel amountsince the sensor indicates that the fuel may provide combustion that istoo lean.

Note that there are various alternative embodiments to the presentdisclosure. For example, the routine may continue the adjustment of fuelbased on sensor 160 even after an engine start. For example, theadjustment can be continued for a predetermined number of seconds afteran engine start, or after a predetermined number of throttle tip-inmaneuvers by the driver. Also note that adjustment of the injected fueland ignition timing based on the sensor 160 can be used for other engineoperating modes than engine starting, such as, for example: during fuelvapor purging, or adaptive learning of the engine sensors 16 and 110.

Note also that in addition to adjust the fuel amount injected, thetiming of the fuel injection can be adjusted based on sensor 160. Forexample, by changing the timing of the fuel injection, it is possible tochange the amount of fuel injected and/or inducted into the engine.Furthermore, depending on the fuel quality, it may be beneficial toinject the fuel at an earlier or later time to reduce emissiongeneration during the combustion process. This is especially true forengines utilized direct injection, where injector 68 is located toinject fuel directly into combustion chamber 30.

In an alternative embodiment, both sensor 160 and dielectric sensor 162are utilized to determine fuel volatility (or viscosity) as indicated inFIG. 3, for example. As an example, sensor 160 provides an indication ofthe fuel DI (or volatility, or stoichiometric air-fuel ratio, etc.)while sensor 162 provides an indication of the ethanol content of thefuel. Then, both the indicated volatility and alcohol content can beused to determine the amount of fuel to be injected during enginestarting. Further, the ignition timing can also be set based on thisdetermination from both sensors 160 and 162. Experimental testing withdifferent fuels and ignition timing values can provide the calibrationdata for such an approach.

Referring now to FIG. 8, an alternative embodiment for adjustinginjected fuel based on sensor 160 is described. In step 810, the routinedetermines whether the engine is in the starting mode. Specifically, theroutine determines whether the engine has exited engine cranking. Whenthe engine has exited engine cranking, the answer to step 810 is “yes”and the routine continues to step 812. In step 812, the routinedetermines an expected engine speed (RPM) based on engine coolanttemperature (ECT) and times since engine starting.

Next, in step 814, the routine measures actual engine rpm based onsensor 118. Then, in step 816, the routine calculates the difference(RPM_dif) between the expected engine speed and the measured actualengine speed. Then, in step 818, the routine determines whether theengine speed difference is greater than a limit (L3). Specifically,limit L3 represents a hysteresis band allowing small changes in enginespeed without control action. When the answer to step 818 is “yes”, theroutine continues to step 820. In step 820, the routine reads signal(FQ) from sensor 160 indicative of the fuel quality. As described above,sensor 160 can provide an indication of fuel viscosity, fuel density,the product of fuel viscosity and density, dynamic fuel viscosity timesdensity, or static fuel viscosity times density. In this particularexample, the sensor 116 provides an indication of dynamic viscositytimes density.

Then, in step 822, the routine determines whether the signal of Q isgreater than a limit L4. In one example, limit L4 is set to 110.199megahertz when using the acoustic wave device described in FIG. 2. Whenthe answer to step 822 is “no”, the routine continues to step 824 andsets the control parameter (K) equal to minus GAIN. Alternatively, whenthe answer to step 822 is “yes”, the routine sets the control parameter(K) equal to plus GAIN in step 826. Next, in step 828, the routinecalculates an adjustment Δ3 based on the feedback parameter K times therpm difference (RPM_DIF). Then, in step 830, the routine adjusts the newfuel injection amount (fueln) based on the base fuel amount minus thecalculated adjustment Δ3. This value is then used to adjust the fuelinjector 68 to deliver the requested fuel amount to the engine.

In still another aspect of the present disclosure, the desired air-fuelratio can be adjusted based on the fuel quality (sensor 160 or acorresponding estimate). For example, the combustion air-fuel ratio istypically feedback controlled based on exhaust gas oxygen sensors, suchas sensor 16, for example. In this case, the amount of injected fuel isadjusted to maintain the desired air-fuel ratio. Thus, according to oneaspect of the present disclosure, this desired air-fuel ratio can beadjusted to compensate for changes related to changes in the fuelquality. In this way, it is possible to obtain improved combustion andreduced emissions by setting the desired air-fuel ratio closer to theactual stoichiometric ratio of the fuel. Further, the air-fuel ratio ofthe combustion gasses can be limited to certain air-fuel ratio ranges toprevent combustion instability. In yet another aspect of the presentdisclosure, this air-fuel limit (typically the lean air-fuel limit) canbe adjusted based on the fuel quality, viscosity, and/or volatility.Such a system is described in FIG. 8B.

In particular, in step 810, the routine determines the desired air-fuelratio set-point based on the fuel quality. Then in step 812, the routinecontrols the injected fuel quantity and/or timing to maintain thedesired value based on the exhaust gas oxygen sensor 16. Then, a limitair-fuel ratio is determined in step 814 based on the fuel quality.Then, steps 816 and 818 prevent the desired value for surpassing thelimit value.

Referring now to FIG. 9, the routine is described for adjusting the lostfuel calculation based on the fuel viscosity. Lost fuel refers to thefuel—does not participate in engine combustion and past the piston ringsof the engine 10. First, in step 910, the routine calculates a base lostfuel parameter based on engine operating conditions as is known in theart. Then, in step 912, the routine adjusts this lost fuel calculationbased on a function of the signal FQ received from sensor 160. The lostfuel parameter (LOST_FUEL) is used to control engine fuel injection andignition timing during engine starting and other operating conditions.

Also note that other fuel calculations can be adjusted based on the fuelquality sensor 160. In particular, transient fuel models can adjust thefuel puddle size and time constant values based on the fuel qualitysensor 160.

Referring now to FIG. 10, the routine is described for performingdefault operation in the case when sensor 160 has degraded. In this way,the engine can provide acceptable combustion even if sensor 160 isdegraded. First, in step 1010 the routine monitors sensor 160 asdescribed herein with respect to FIGS. 11 through 13. Next, in step1012, the routine determines whether sensor 160 is degraded. When theanswer to step 1012 is “no”, the routine returns to step 1010.

When the answer to step 1012 is “yes”, the routine continues to step1014 and sets the signal FQ received from sensor 160 to a default value(for example 110.193 megahertz) which can then be used in the fuelstarting control routines described above herein. In other words, theroutine ignores the actual sensor output and replaces this actual sensoroutput with a predetermined default value. Further, in step 1016, theroutine lights an indicator light to notify the driver of the degradedsensor.

In this way, it is possible to continue acceptable engine combustioneven when the fuel quality sensor provides a degraded output. Thedefault value selected to be used in this case represent values that areleast likely to result in degraded engine combustion irrespective of thefuel quality actually in tank 140.

Referring now to FIG. 11, the routine is described for determining thedegradation of sensor 160. In general terms, the routine uses estimatesof combustion air-fuel ratio during cold and warm engine operatingconditions to determine an estimated fuel quality value which is thencompared to the sensor reading to determine whether the sensor hasdegraded.

First, in step 1110, the routine determines whether engine coolanttemperature is less than a threshold (L5) and whether the engine speedand load are in a first predetermined range (R1). When the answer tostep 1110 is “yes”, the routine continues to step 1112 and saves theadaptive air-fuel ratio term as AT1. The adaptive air-fuel term is basedon long term adaptive learning via sensor 16.

Next, in steps 1114 and 1116, this is repeated for warm engine operatingconditions (ECT greater than L6) and this time the adaptive term issaved as AT2. Next, in step 1118, the routine determines whether bothAT1 and AT2 have been updated via steps 1112 and steps 1116. When theanswer to step 1118 is “no”, the routine returns to the start. When theanswer to step 1118 is “yes”, the routine continues to step 1120.

Continuing with FIG. 11, in step 1120 the routine calculates thedifference of (ΔT) between the first and second saved adaptive terms.This represents a change in combustion air-fuel ratio between cold andwarm engine coolant temperatures within a defined engine speed range R1.Next in step 1122 the routine estimates a sensor reading (FQ_EST) basedon the calculated difference ΔAT. Then, in step 1124, the routinecompares the estimate with the sensor reading and indicates whetherdegradation has been detected. In particular, the routine determineswhether the difference between the estimate and the actual sensorreading is greater than a predetermined amount for a predeterminedduration. When this occurs, the routine provides an indication to thedriver via an indicator light.

Referring now to FIG. 12, an alternate embodiment for determiningdegradation in sensor 160 is described. First, in step 1210 the routinemonitors the rpm difference from step 816 of FIG. 8. In particular, theroutine monitors the rpm difference over numerous engine starts andaverages this value with a predetermined averaging filter rate. Then instep 1212, the routine estimates the sensor output (FQ) based on theaverage rpm difference over these monitored engine cold starts. In oneexample, the routine monitors between 15 to 20 engine cold starts toprovide an estimate of the sensor output. Alternatively, more or lessengine starts can be utilized depending on the required accuracy. Then,in step 1214, the routine compares the estimate with the actual sensorreading as described above herein with particular reference to step1124.

Referring now to FIG. 13, yet another alternative embodiment fordetermining degradation in sensor 160 is described. In particular, thisroutine monitors the sensor output over time and detects suspiciouslyconstant sensor output, or suspiciously large changes in sensor output.

First, in step 1310, the routine monitors the signal sensor output (FQ)over various engine starts. Next, in step 1312, the routine determineswhether the sensor reading has changed by less than a threshold (L7)over these engine starts. As above, approximately 10 to 15 engine startscan be utilized. As above, more or less engine starts can be utilizedbased on the required accuracy. In particular, in step 1312, the routinemonitors the sensor reading over several fuel tank refills. If thesensor reading has not changed over various starts and refills, theroutine determines that the sensor has degraded in step 1316 asdescribed above herein with particular reference to 1124 indicates thisto the driver via an indicator light.

When the answer to step 1312 is “no”, the routine continues to step1314. In step 1314, the routine determines whether the sensor readinghas changed by greater than a predetermined amount (L8) over variousengine starts. If the sensor reading changes greater than this amount,the routine indicates degradation in step 1316 as described above.

Still another alternative embodiment, that can be used alone or inaddition to the above described approaches, would use a purposefuldisturbance of the amount of injected fuel during idle conditions. Thereshould be no effect if the sensor is measuring accurately. If the sensoroutput is degraded, then a further deviation will result in an rpmfluctuation.

Note that the estimates in FIGS. 11-14 (as well as in FIG. 17B) can beused in place of the sensor reading in an alternative embodiment.

Referring now to FIG. 14, a routine is described for adjusting fuelvapor purging estimation and control based on sensor 160. First, in step1410, the routine determines whether the engine is currently purgingfuel vapors from the fuel system. When the answer to step 1410 is “Yes”,the routine continues to step 1412 and estimates the vapor concentrationbased on various sensors, such as for example: oxygen sensor 16, massair flow sensor 110, command signal (PRG), and command signal (FPW).Various methods are known for estimating fuel vapor concentration andcan be used in step 1412.

Next, in step 1414, the routine adjusts the estimate based on the fuelquality signal FQ from sensor 160. In particular, the routine adjuststhe amount of fuel vapors estimated by shifting the assumedstoichiometric combustion air-fuel ratio to account for the output fromsensor 160. In this way, the routine can re-calculate the fuel vaporquantity using this additional information. Then, in step 1416, theroutine can adjust the fuel pulse with and purge control valve based onthis adjusted estimate of fuel vapor concentration to more accuratelycontrol engine combustion.

In addition, an estimate of the fuel vapor concentration coming from thetank (before feedback information becomes available) can be determinedbased on the fuel quality.

FIG. 15 shows in detail how the liquid fuel interacts with the acousticwave, the amplitude of which is shown as 1510. This illustrates how thewave generated by the oscillator circuit propagates into the liquid,thereby creating the basic sensing ability of the device. Thisinteraction is influenced by the liquid density and viscosity.

FIG. 16 shows a routine for adjusting the engine fuel control dependingon whether the fuel used is methanol (M85), or gasoline fuel. As shownin FIG. 4, sensor 160 can be used (alone or in conjunction with sensor162) to indicate such fuel type information. First, in step 1610, theroutine measures the sensor output (FQ). Then, in step 1612, the signal(FQ, or viscosity*density depending on the type of sensor used) iscompared with a value (Limit, 110.16 MHz in this example). When theanswer to step 1614 is YES (i.e., FQ is less than the Limit), theroutine indicates methanol fuel in step 1614. Alternatively, in step1616, the routine indicates gasoline fuel. Then, in step 1620, theroutine controls the injected fuel based on the indicated fuel type.Furthermore, the routine can adjust the ignition timing based on thefuel type, if desired.

Referring now to FIGS. 17A and 17B, yet another embodiment of a methodfor estimating fuel quality is illustrated. In particular, FIG. 17Bshows a method utilized fuel vapor learning to estimate fuel volatility.In FIG. 17B, the routine first enables purge compensation and disablesadaptive learning in step 1710. In other words, the routine assigns allof the air-fuel error to determining the concentration of fuel vapors(pcomp) in the purge flow. Typically, pcomp is the learned concentrationbased on the MAF sensor, fpw, and exhaust gas oxygen sensors, as isknown in the art.

Next, in step 1712, the routine ramps open the purge valve. Step 1714continues the ramping until the valve is fully open. When fully open,the routine continues to step 1716 to determine whether a timer (time)has run (i.e., reached limit time T2). If not, the routine continues tostep 1718 to monitor the learned concentration value (pcomp) over thisinitial time period. In particular, in step 1720, the routine calculatesthe rate of change (R) of the purge concentration and estimates (in step1722) the fuel quality/volatility (FQ_est) based on the calculated rate(R).

As shown in FIG. 17A, this calculated rate is taken during a fixedvolumetric flow since the purge valve is fully open at time t1. Thisrate may provide an indication of fuel desorption or vaporization fromthe fuel tank and therefore can be correlated to volatility. However, inan alternative embodiment, the rate of change can be normalized withmass airflow to reduce changes in mass airflow from altering the pcomprate of change or slope. Otherwise, the slope may be influenced by massairflow changes. Note also that the rate of change may be correlated toa range of fuel volatility, such as for example, it may be broken downinto an indication of high volatility, medium volatility, or lowvolatility.

As such, the learning based on the liquid injected fuel is disabled andthe learning of the fuel quality based on vaporized fuel is enabled.

Also note that the learning of the fuel quality can be enabled after asecond period (after the valve is fully open) to eliminate degradedreading from the stored vapors in the tank. By enabling learning of thefuel quality based on the rate of change after the stored vapors havebeen purged, a better reading of the fuel vaporization rate can befound.

In still another embodiment, the learning of the fuel quality (or blend)can be enabled after a purge canister is blocked (or partially blocked)from providing fuel vapors to the intake manifold (e.g., via a solenoidvalve). This may be used in a configuration such as when third canister147 and valve 149 are present. In this way, airflow through the canisteris reduced (or stopped) during the determination of fuel quality orblend in the generated tank vapors, so that effects of desorbed fuelvapors from the canister may be reduced.

As described above, the present disclosure uses a determination of fuelvolatility (viscosity in one example) to predict the combustioncharacteristics of the fuel during cold engine starting. This predictioncan include compensation for various parameters, such as fueltemperature, engine temperature, barometric pressure, atmospherictemperature, intake air temperature, and others. In any event, theengine controller is able to adjust the amount of scheduled fuel (orscheduled air-fuel mass ratio) based on the sensed data. This allows fora tighter control of combustion air and fuel (thereby improving engineemissions even for “normal” fuels). In addition, it allows for improvedengine startability and driveability, even when so called “fringe”fuels, such as high or low DI fuels are experienced in the engine. Inthis way, a feedfoward estimate of the fuel quality can be obtainedwithout waiting for dips in engine speed.

A fuel vapor volatility indication may also indicate fuel blend. Forexample, ethanol, or an ethanol gasoline mixture, may have highervolatility than gasoline. This may then be used in multi-fuel vehiclesto indicate fuel blend, and then used to control the engine, or be usedin diagnostics. There are likely many other uses for a fuel vaporvolatility indication (measured or estimated). For example, evaporationof the manifold fuel puddle may be influenced by fuel vapor volatility.Therefore, a fuel vapor volatility indication may be used to determinerate of evaporation in a transient fuel algorithm, and thus used toadjust fuel injection during transient fuel operation.

Further, with a combination of a viscosity-density sensor and adielectric sensor, one can measure both the DI and amount of ethanolpresent in the fuel.

In yet another aspect of the present disclosure, the method uses aviscosity-density sensor to measure large concentrations of alcohol ascan be present in flex fuels (0-85% ethanol).

Note that various embodiments have been described for determining fuelquality, volatility, and/or viscosity. In one example, an acoustic wavesensor uses acoustic energy to determine fuel viscosity, which is thenused to determine fuel combustion quality. In another embodiment, thefuel quality is estimated from adaptive parameters based on exhaust gasair-fuel ratio sensors. In still another embodiment, the rate of changeof exhaust gas sensors is utilized to estimate fuel volatility, andthereby estimate fuel quality.

Another advantageous use of fuel volatility relates to fuel tank leakdetection and diagnostics. Specifically, in one example, a measurementor estimate of fuel volatility can be used in determining leaks in thefuel system, such as the fuel tank or fuel rail, for example. In oneembodiment, where pressure is monitored in a sealed fuel system afterthe engine is stopped, a fuel volatility determination can be used toenable, disable, or modify a leak detection test. The fuel system can besealed by closing vent valves, such as the optional valves included incanisters 144 and 146, as well as valve 149. In one example, after theengine is stopped (off) and the system is sealed, pressure (andoptionally temperature) in the fuel system can be expected to change(increase) due to heat transfer into the tank (from the environmentand/or vehicle), or

For example, a volatility indication may be used during on-boarddiagnostics to abort or prevent fuel system diagnostics when fuel vaporvolatility is high. Otherwise, the high pressure caused by high fuelvapor volatility may mask detecting fuel vapor leakage.

This concludes the detailed description.

1. A method of determining degradation of a fuel system including a fueltank of a vehicle having an engine, the method comprising: purging fuelvapors generated in the tank in the engine; determining an indication offuel volatility during said purging operation; and enabling detection ofdegradation of the fuel system after the engine is stopped based on saidindication.
 2. The method of claim 1 wherein said purging is performedduring engine operation.
 3. The method of claim 1 further comprising,during purging, adjusting a fuel injection amount based on feedback froman exhaust gas oxygen sensor in an engine exhaust to obtain a desiredair-fuel ratio.
 4. The method of claim 3 wherein said indication isbased on said feedback.
 5. The method of claim 1 wherein said indicationis based on a rate of change of estimate fuel vapors.
 6. The method ofclaim 1 wherein said indication is adjusted based on mass air flow. 7.The method of claim 1 wherein said indication is affected by a purgevalve position.
 8. The method of claim 1 wherein degradation detects aleak in said fuel system based on changes in pressure in said fuelsystem after the engine is stopped.
 9. The method of claim 8 whereinsaid degradation further includes closing a valve in said fuel system.10. A method of determining degradation of a fuel system including afuel tank of a vehicle having an engine, the method comprising: purgingfuel vapors generated in the tank in the engine; determining anindication of fuel volatility during said purging operation that isaffected by a rate of change of fuel vapor during said purging; andadjusting engine operation based on said indication.
 11. The method ofclaim 10 wherein said adjusting engine operation includes enablingdetection of degradation of the fuel system after the engine is stopped.12. The method of claim 10 wherein said adjusting engine operationincludes adjusting a fuel injection amount during engine starting.
 13. Amethod of determining degradation of a fuel system including a fuel tankof a vehicle having an engine, the method comprising: purging fuelvapors generated in the tank in the engine when fuel vapor entering theengine from a fuel system canister are below a threshold; determining anindication of fuel volatility during said purging operation; andenabling detection of degradation of the fuel system after the engine isstopped based on said indication.
 14. A system for a mobile vehiclehaving an engine, comprising a fuel tank; a fuel system valve coupled tothe fuel tank, said valve coupled between an environment of the vehicleand said tank; a fuel system canister coupled in the system; an exhaustgas sensor coupled in an engine exhaust; and a controller for purgingfuel vapors generated in the tank in the engine while the engine isperforming combustion, determining an indication of fuel volatilitybased on said purging operation; and enabling detection of degradationof the fuel system after the engine is stopped based on said indication.15. The system of claim 14, wherein during said determining, said fuelsystem canister is blocked from the engine.